1. Field of the Invention
The present invention relates to anti-microbial solutions and methods of making and using anti-microbial solutions, especially sporicidal solutions.
2. Background of the Invention
Steam autoclaves can be used to sterilize some medical instruments by subjecting the instruments to superheated steam at high pressures before being depressurized and cooled. One of the drawbacks of the steam autoclave is that many medical instruments cannot withstand the high temperatures and pressures. Another drawback resides in the one to two hour cycle time that is required to achieve sterilization.
Ethylene oxide gas can be used to sterilize some other medical instruments and equipment that cannot withstand the pressure or temperature of the autoclave. The instruments are sealed in a sterilizing chamber and pressurized with the ethylene oxide gas. However, ethylene oxide sterilization requires long cycle times and careful handling of the highly toxic ethylene oxide gas. Furthermore, some medical equipment can not be sterilized with ethylene oxide gas.
Liquid sterilization systems can be used to sterilize equipment that cannot withstand either the autoclave or the ethylene oxide gas. These systems involve immersing the equipment into a vat or tank that has been filled with a sterilizing solution, such as stabilized hydrogen peroxide or glutaraldehyde. Because such liquid sterilizations are normally performed manually, the skill and care of the technician are determining factors in whether sterilization or disinfection is, in fact, attained. In many instances, the components of the anti-microbial composition must be mixed by a technician who may become exposed to the harmful vapors produced by many disinfectants, such as glutaraldehyde. Even when mixed properly, immersion times on the order of six to ten hours are commonly required to assure sterilization. Moreover, many liquid sterilization systems are highly corrosive to metal parts, particularly brass, copper, and aluminum. With long immersion times, even the carbon steel and stainless steel of the medical instruments can become pitted and sharp cutting edges dulled.
Antimicrobial compositions are particularly needed in the food and beverage industries to clean and sanitize processing facilities such as pipelines, tanks, mixers, etc. and continuously operating homogenization or pasteurization apparatus. Other uses for antimicrobial compositions include vegetable washing and disinfection, meat surface decontamination, poultry chiller baths, cleaning of electronic components, treatment of wounds, cleaning in place of food processing equipment, cleaning and disinfecting beverage containers, terminal sterilization, treatment of contaminated infectious waste and elimination of odors.
Sanitizing compositions have been formulated in the past to combat microbial growth in such facilities. For example, Wang, U.S. Pat. No. 4,404,040, teaches a short chain fatty acid sanitizing composition comprising an aliphatic short chain fatty acid, a hydrotrope solubilizer capable of solubilizing the fatty acid in both the concentrate and sanitizing solution, and a hydrotrope compatible acid so that the sanitizing solution has a pH in the range of 2.0 to 5.0.
Ozone has long been recognized as a useful chemical commodity valued particularly for its outstanding oxidative activity. In fact, ozone is the fourth strongest oxidizing chemical known, having an oxidation potential of 2.07 volts. Because of this property, ozone and/or fluid mixtures including ozone are capable of removing a wide variety of contaminants, such as cyanides, phenols, iron, manganese, and detergents, from surfaces. Also, ozonated water is used to xe2x80x9ccleanxe2x80x9d, i.e., oxidize, the surface of silicon wafers in-process in the semiconductor industry. Additionally, ozone is also useful for inhibiting, reducing and/or eliminating the accumulation of biomass, mold, mildew, algae, fungi, bacterial growth and scale deposits in various aqueous solution systems. When used in this manner, ozonation provides the advantage of producing a lesser quantity of potentially harmful residues than, e.g., chlorination, which leaves undesirable chlorinated residues in aqueous systems. However, the effectiveness of ozonated water in each of these applications is adversely affected by its low solubility and short-half life (approximately 10 minutes) in aqueous solutions. That is, not only is it difficult to dissolve ozone in an aqueous solution, but also, once dissolved, it is difficult to maintain the ozone in solution.
Ozone has been shown to be inadequate for many medical disinfection and sanitization applications. The disinfection of medical equipment often necessitates use of disinfectants able to deactivate resistant microorganisms, such as bacterial spores. Ozone is a poor sporicidal agent both in the gas phase or dissolved in liquids. This is believed to be due to the slow penetration of ozone through the spore""s protective layers. Though this deficiency can be overcome by lengthening the contact time, it is inconvenient and often impractical to do so. Furthermore, ozone does not retain its antimicrobial activity in the presence of interfering compounds, because ozone reacts indiscriminately with dissolved oxidizable substances such that the amount of ozone available for disinfection is drastically reduced.
To counter these limitations, there are several methods of increasing the quantity of dissolved ozone in aqueous solutions, each of these prior art methods has limitations that render them inadequate for certain applications. For example, bubbling ozone directly into water at ambient pressure has been used as a method to dissolve ozone in aqueous solutions. Such a technique, however, does not optimize the quantity of ozone dissolved, since the ozone bubbles effervesce before a substantial amount of ozone can be dissolved into solution and/or before the ozonated water can be applied to the surface to be treated.
European patent application No. EP 0 430 904 A1 discloses a process for producing ozonated water comprising the step of contacting an ozone-containing gas with fine droplets of water. However, this process is less than optimal since it provides limited contact between the ozone-containing gas and water. Additionally, this application does not teach a method of keeping the ozone in solution until it is delivered to a point of use. Thus, it is possible that, upon delivery, a large quantity of the ozone dissolved in solution will effervesce, and the benefits of the mixing process will be lost.
Several methods utilizing cooling to increase the quantity of dissolved ozone in aqueous solutions have also been proposed. For example, U.S. Pat. No. 5,186,841 discloses a method of ozonating water comprising injecting ozone through an aqueous stream across a pressure drop of at least 35 psi. The ozonated stream is then combined with a second stream that is preferably a portion of an aqueous solution that is recirculating in a cooling water system. The resultant stream is forced to flow at a velocity of 7 feet per second for a distance sufficient to allow 70% of the ozone to be absorbed. Additionally, U.S. Pat. No. 4,172,786 discloses a process for increasing the quantity of dissolved ozone in an aqueous solution by injecting an ozone containing gas into a side stream conduit that circulates a portion of cooling water. U.S. Pat. No. 5,464,480 discloses a process for removing organic materials from semiconductor wafers using ozonated water. Specifically, this patent teaches that high ozone concentration water, suitable for use in the disclosed process may be obtained by mixing ozone and water at a temperature of from about 1xc2x0 C. to 15xc2x0 C.
The use of pressurized vessels and distribution systems is also a known method of improving the level of dissolved ozone. A system disclosed in U.S. Pat No. 5,971,368 describes a system where by introducing a gas into a pressurized vessel containing a liquid; delivering the resulting admixture to a point of use through a pressurized conduit; and subjecting the admixture to controlled dispensing at the point of use, the quantity of dissolved gas in the liquid is not only enhanced over the quantity of dissolved gas in the liquid at atmospheric pressure, but also, that a substantial portion of the enhanced amount of dissolved gas stays in solution to the point of use.
U.S. Pat. No. 5,662,803 (P. R. Young, Nalco Corporation) discloses use of ozone combined with compounds normally added to water called scale inhibitors, preventing ozone from degrading certain water treatment chemicals. In one example however, (example 5) they examine the effect of ozone combined with an organic additive against bacteria suspended in solution. The bacteria are in a phosphate solution and the additive is propionate (non acid form). The propionate reduces the decay rate of ozone. The example shows that the ozonated propionate solution is more effective against bacteria.
U.S. Pat. No. 5,484,549 describes using ozone introduced into an aqueous solution containing Lewis base compounds. Such bases include sodium hydroxide, potassium hydroxide, sodium orthosilicate, sodium tripolyphosphate, sodium carbonate and sodium bicarbonate. The solutions provide an enhanced surface cleaning effect. A continuation of this patent (U.S. Pat. No. 5,567,444) describes an aqueous cleaning solution that is used as a first treatment, combined with a second liquid containing peroxyacids. The two compositions used consecutively provide improved surface cleaning and surface decontamination.
Numerous inventions relate to the ozonolysis of organic compounds that contain nonaromatic carbon-carbon double bonds. The formation of peroxidic species by ozonolysis of oleic acid is described by Rebovic et al (JAOCS Vol 69, February 1992). This type of ozonolysis reaction is a useful step in the industrial production of carboxylic acids. Typically, the olefinic starting compounds are treated in a solvent with an ozone-containing carrier gas. If the reaction is carried out in aprotic solvents, secondary ozonides are formed. In protic solvents, such as for example alcohols or acids, peroxides are formed, which can occur as polymers. German patent No. 2,713,863 discloses a method of continuously producing an ozonide by ozonizing a high molecular weight olefin oleic acid or linoleic acid in the presence of ester and an organic acid or alcohol. Kigawa et al U.S. Pat. No. 5,292,941 discloses a method for ozonizing an unsaturated fatty acid or a lower alkyl ester thereof providing, amongst other things, efficient removal of the reaction heat. It is usual to further react the ozonolysis products with oxidants to form carboxylic acids. Sometimes peroxyacids are used as the oxidants. Kulpe et al in U.S. Pat. No. 5,591,893 describes such as process emphasizing the role of hydrogen peroxide in the oxidative work up.
Ozonized sunflower oil xe2x80x9cOleozonxe2x80x9d has been shown to have antimicrobial effects on bacterial, viruses and fungi (Lezcano et al., Ozone Sci. Engineering 22 (2000) 207-214). Ozone reacts with unsaturated fatty acids present in the oil, and targets carbon-carbon double bonds. Substances produced include hydrogen peroxide aldehydes alpha dihroxy-hydroperoxides and Criegee ozonides. This substance can be applied as a skin treatment agent.
As the term xe2x80x9csanitizingxe2x80x9d is used in the method of the present invention, it means a reduction in the population numbers of undesirable microorganisms by about 5 powers (i.e., at least 5 orders of magnitude). The composition may also be used to achieve disinfection or sterilization (i.e., elimination of all microorganisms) by employing higher levels of active biocides in the use solutions. Disinfection and sterilization are truly lethal in their effects. It is to be emphasized that at the lesser strengths the instant use solution provides sanitizing performance. At still lesser strengths, the present invention provides a xe2x80x9cbiostaticxe2x80x9d capability where the organisms, in the presence of the agent are inhibited from growing but upon removal from the agent, it can again multiply.
The invention includes a method of preparing an antimicrobial solution, comprising the step of ozonating a solution comprising greater than 80 weight percent ethanol and more preferably between 90 and 100 weight percent ethanol. It is suitable to obtain the ethanol from common sources and in common forms, specifically including hydrous (water-containing) ethanol. Optionally, the solution further comprises octanoic acid, preferably between 1 and 40 percent, more preferably between 5 and 25 percent. It is preferable to ozonate the solution until the solution has an oxidation potential of greater than 550 mV. Optionally, the method may include the further step of diluting the ozonated solution with water to a water/ozonated solution ratio of between 1 and 100, preferably between 3 and 81. Preferably, the solution is characterized by sporicidal activity. Finally, the method may optionally include the step of contacting a microbially contaminated surface with the diluted solution. Preferably, the surface is then rinsed to remove the solution.
The invention also includes a method of preparing an antimicrobial solution, comprising the steps of preparing a mixture comprising one or more short chain saturated fatty acids having from 1 to 4 carbon atoms and one or more long chain saturated fatty acids having 5 or more carbon atoms, and ozonating the mixture. The preferred short chain saturated fatty acid is acetic acid and the preferred long chain saturated fatty acid is octanoic acid. In one particularly preferred solution, the mixture comprises between 10 and 20 weight percent octanoic acid and between 80 and 90 weight percent acetic acid. Optionally, the method may further comprise diluting the ozonated mixture with water or other solvent, preferably where the volumetric ratio of the water relative to the ozonated mixture is between 1 and 100. The antimicrobial solution is most preferably sporicidal.
The methods of the present invention may further comprise the steps of measuring the oxidation potential of the mixture, and continuing to ozonate the mixture until the measured oxidation potential is greater than a setpoint, such as about +550 mV. Further, it is optional to electrochemically produce the ozone as needed to ozonate the mixture.
With respect to certain organic compounds, such as octanoic acid, it is preferred that the precursor solution not be diluted before or during ozonolysis, but rather may be substantially diluted following ozonolysis. While these precursor solutions can tolerate minor amounts of water, it is preferred that these solutions be substantially free of water. However, after the mixture or solution has been ozonated, the ozonated mixture may be freely diluted with water while retaining its antimicrobial or sporicidal activity. By contrast, other organic compounds, such as ethanol, are substantially unaffected by the presence of water during ozonolysis.